The invention relates to a method of measuring the amount of abrasive material in a fluid flow of liquid and/or gas. The method can, for example, be employed to supervise the production rate of sand in an oil and/or gas production well.
Production of oil and gas often results in that the produced oil and gas contains sand. For production wells in a sandstone reservoir without a sand controlling system it is assumed that more than 25 ppm of quartz particles with diameter of 1-1000 .mu.m may be produced. If a sand controlling system is employed, sand production will be approximately 25 ppm with a diameter of 0-100 .mu.m. Sand production cannot only cause severe erosion of the production equipment, but large quantities of sand can also be accumulated in the equipment and result in production break down. If the production of said is measured reliably, the production rate can be adjusted and the problems relating to erosion and accumulation of sand can be reduced. The maximum production rate without producing sand can thus be established. Therefore, there is a need to monitor small/medium said production rates with either small particles (applying gravel packs) or with a full spectrum of the particle size. Monitoring should preferably be applied on each individual well. There are also various other applications where continuous supervision is important when there is danger of contamination of abrasive materials in fluid flows.
Different systems have been used or suggested for monitoring or detecting said content in a fluid well. One system to employ in a fluid flow to determine abrasion caused by sand is an erosion probe. Sand can erode, for example, a thin, hollow-walled probe which is mounted in the fluid flow. A pressure difference between the fluid flow and a reference point will activate an alarm. Therefore, there will be a considerable time delay before this probe detects sand, and it will not give continuous monitoring of the sand content in the fluid flow or of the sand production rate.
There are also known different acoustic probes that either can be clamped on the outside of a pipe wall or mounted inside the pipe. This probe can detect said production in either a gas or a liquid flow. The ability to distinguish between sand noise and other noise is not satisfactory in intermittent or annular/mist fluid flows. Calibration of the acoustic probe has to be performed with actual production parameters and by injection of said. The calibration will change when the production rate or other sources of noise are varied.
Small particles (0-0.5 mm dia.) produce acoustic energy too low to discriminate between particle- and flow noise. One such acoustic probe is described in NO Patent No. 140,838.
From U.S. Pat. No. 3,678,273, 3,767,916 and EP Patent No. 0 317 339 disclose various methods for measuring erosion caused by abrasive fluid. Common for these known methods is that a detector coated with a radioactive material is positioned in a fluid flow, for example an oil slurry. The detector is activated by radiation from the radioactive coating due to a thickness reduction caused by the abrasive fluid, the detector is in contact with a control and monitoring unit on the outside of the pipe. The particle concentration of the flow is determined by determining the particle in a concentration of an equivalent flow of known composition which causes the measured reduction of radiation emission when it contacts an equivalent material at the measured flow velocity.
The particle concentration in the flow can thus be estimated. The detector is mounted in the flow and will be an obstruction to the flow. The detector will not be able to detect small particles because these particles will follow the flow and pass around the obstruction. This detector can therefore not be used in a high pressure hydrocarbon pipe where it is impossible to predict the sand distribution. The accuracy and how the particle content is measured are not discussed. The method requires calibration and a uniform distribution of the abrasive particles.